Formulation of CTOD design curve considering the yield to tensile ratio

Abstract

The Crack Tip Opening Displacement (CTOD) design curve approach is one of the fracture assessment procedures for estimating CTOD as an elastic-plastic fracture driving force, and is used for the assessment of flaws in welded structures. The Japan Welding Engineering Society (JWES) has produced a semi-empirical CTOD design curve, where CTOD is calculated from the local strain acting on the assumed crack, the crack size and the yield strain of the material. CTOD should be estimated by using all the factors influencing the crack driving force in the welded joint, but the yield to tensile ratio, Y/T, which relates to strain hardening behavior, is not used for the CTOD design curve. On the other hand, the new CTOD calculation formula adopted by the JWES CTOD fracture toughness testing standard uses Y/T, and derived CTOD values from the formula are affected by Y/T. Consequently, there is a mismatch in CTOD calculation between the fracture driving force of welded structures and the fracture toughness of standard specimens. In this study, Y/T was considered for formulating a new CTOD design curve. CTOD estimated by the new design curve was compared with CTOD obtained by the finite element analysis of a corner boxing fillet welded joint. The new CTOD design curve contributes to a good CTOD estimation for different Y/T welded joint models.